<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    

    <style>
        .box {
          position: relative;
          height: 300px;
          width: 300px;
          background-color: lightblue;

          text-align: center;
          border-radius: 10%;
          overflow: hidden;
        }
    
        .box-in {
          visibility: visible;
          display: inline-block;
          height: 200px;
          width: 200px;
          margin-top: 100px;
          border: 3px solid black;
          border-color: white transparent transparent white;
          transform: rotate(45deg);
        }
    
        .box:hover:before {
          top: 50%
        }
    
        .box:hover .box-in {
          visibility: hidden;
        }
    
        .box:before {
          position: absolute;
          top: -50%;
          left: 50%;
          transform: translate(-50%, -50%);
          content: '回到顶部';
          width: 300px;
          font-size: 110px;
          color: whitesmoke;
          font-weight: bold;
        }
      </style>
      <div id="box" class="box">
        <div class="box-in"></div>
      </div>



      <h1>回到顶部(without JavaScript )</h1>
      
      
</body>
</html>